SQL input consists of a sequence of commands. A command is composed of a sequence of
tokens, terminated by a semicolon
(";"). The end of the input stream
also terminates a command. Which tokens are valid depends on the
syntax of the particular command.

A token can be a key word, an
identifier, a quoted identifier, a literal (or constant), or a special character
symbol. Tokens are normally separated by whitespace (space, tab,
newline), but need not be if there is no ambiguity (which is
generally only the case if a special character is adjacent to
some other token type).

This is a sequence of three commands, one per line (although
this is not required; more than one command can be on a line, and
commands can usefully be split across lines).

Additionally, comments can occur in
SQL input. They are not tokens, they are effectively equivalent
to whitespace.

The SQL syntax is not very consistent regarding what tokens
identify commands and which are operands or parameters. The first
few tokens are generally the command name, so in the above
example we would usually speak of a "SELECT", an "UPDATE",
and an "INSERT" command. But for
instance the UPDATE command always
requires a SET token to appear in a
certain position, and this particular variation of INSERT also requires a VALUES in order to be complete. The precise syntax
rules for each command are described in Part VI.

Tokens such as SELECT, UPDATE, or VALUES in the
example above are examples of key
words, that is, words that have a fixed meaning in the SQL
language. The tokens MY_TABLE and
A are examples of identifiers. They identify names of tables,
columns, or other database objects, depending on the command
they are used in. Therefore they are sometimes simply called
"names". Key words and identifiers
have the same lexical structure, meaning that one cannot know
whether a token is an identifier or a key word without knowing
the language. A complete list of key words can be found in
Appendix C.

SQL identifiers and key words must begin with a letter
(a-z, but
also letters with diacritical marks and non-Latin letters) or
an underscore (_). Subsequent
characters in an identifier or key word can be letters,
underscores, digits (0-9), or dollar signs ($). Note that dollar signs are not allowed in
identifiers according to the letter of the SQL standard, so
their use might render applications less portable. The SQL
standard will not define a key word that contains digits or
starts or ends with an underscore, so identifiers of this form
are safe against possible conflict with future extensions of
the standard.

The system uses no more than NAMEDATALEN-1 bytes of an identifier; longer
names can be written in commands, but they will be truncated.
By default, NAMEDATALEN is 64 so the
maximum identifier length is 63 bytes. If this limit is
problematic, it can be raised by changing the NAMEDATALEN constant in src/include/pg_config_manual.h.

Key words and unquoted identifiers are case insensitive.
Therefore:

UPDATE MY_TABLE SET A = 5;

can equivalently be written as:

uPDaTE my_TabLE SeT a = 5;

A convention often used is to write key words in upper case
and names in lower case, e.g.:

UPDATE my_table SET a = 5;

There is a second kind of identifier: the delimited identifier or quoted identifier. It is formed by enclosing an
arbitrary sequence of characters in double-quotes ("). A delimited identifier is always an
identifier, never a key word. So "select" could be used to refer to a column or
table named "select", whereas an
unquoted select would be taken as a
key word and would therefore provoke a parse error when used
where a table or column name is expected. The example can be
written with quoted identifiers like this:

UPDATE "my_table" SET "a" = 5;

Quoted identifiers can contain any character, except the
character with code zero. (To include a double quote, write two
double quotes.) This allows constructing table or column names
that would otherwise not be possible, such as ones containing
spaces or ampersands. The length limitation still applies.

A variant of quoted identifiers allows including escaped
Unicode characters identified by their code points. This
variant starts with U& (upper or
lower case U followed by ampersand) immediately before the
opening double quote, without any spaces in between, for
example U&"foo". (Note that this
creates an ambiguity with the operator &. Use spaces around the operator to avoid
this problem.) Inside the quotes, Unicode characters can be
specified in escaped form by writing a backslash followed by
the four-digit hexadecimal code point number or alternatively a
backslash followed by a plus sign followed by a six-digit
hexadecimal code point number. For example, the identifier
"data" could be written as

U&"d\0061t\+000061"

The following less trivial example writes the Russian word
"slon" (elephant) in Cyrillic
letters:

U&"\0441\043B\043E\043D"

If a different escape character than backslash is desired,
it can be specified using the UESCAPE
clause after the string, for example:

U&"d!0061t!+000061" UESCAPE '!'

The escape character can be any single character other than
a hexadecimal digit, the plus sign, a single quote, a double
quote, or a whitespace character. Note that the escape
character is written in single quotes, not double quotes.

To include the escape character in the identifier literally,
write it twice.

The Unicode escape syntax works only when the server
encoding is UTF8. When other server
encodings are used, only code points in the ASCII range (up to
\007F) can be specified. Both the
4-digit and the 6-digit form can be used to specify UTF-16
surrogate pairs to compose characters with code points larger
than U+FFFF, although the availability of the 6-digit form
technically makes this unnecessary. (Surrogate pairs are not
stored directly, but combined into a single code point that is
then encoded in UTF-8.)

Quoting an identifier also makes it case-sensitive, whereas
unquoted names are always folded to lower case. For example,
the identifiers FOO, foo, and "foo" are
considered the same by PostgreSQL, but "Foo" and "FOO" are
different from these three and each other. (The folding of
unquoted names to lower case in PostgreSQL is incompatible with the SQL
standard, which says that unquoted names should be folded to
upper case. Thus, foo should be
equivalent to "FOO" not "foo" according to the standard. If you want to
write portable applications you are advised to always quote a
particular name or never quote it.)

There are three kinds of implicitly-typed constants in PostgreSQL: strings, bit strings, and
numbers. Constants can also be specified with explicit types,
which can enable more accurate representation and more
efficient handling by the system. These alternatives are
discussed in the following subsections.

A string constant in SQL is an arbitrary sequence of
characters bounded by single quotes ('), for example 'This is a
string'. To include a single-quote character within a
string constant, write two adjacent single quotes, e.g.,
'Dianne''s horse'. Note that this is
not the same as a
double-quote character (").

Two string constants that are only separated by whitespace
with at least one
newline are concatenated and effectively treated as if
the string had been written as one constant. For example:

SELECT 'foo'
'bar';

is equivalent to:

SELECT 'foobar';

but:

SELECT 'foo' 'bar';

is not valid syntax. (This slightly bizarre behavior is
specified by SQL;
PostgreSQL is following the
standard.)

PostgreSQL also accepts
"escape" string constants, which
are an extension to the SQL standard. An escape string
constant is specified by writing the letter E (upper or lower case) just before the
opening single quote, e.g., E'foo'.
(When continuing an escape string constant across lines,
write E only before the first
opening quote.) Within an escape string, a backslash
character (\) begins a C-like
backslash escape sequence, in which
the combination of backslash and following character(s)
represent a special byte value, as shown in Table
4-1.

Table 4-1. Backslash Escape Sequences

Backslash Escape Sequence

Interpretation

\b

backspace

\f

form feed

\n

newline

\r

carriage return

\t

tab

\o, \oo,
\ooo (o = 0 - 7)

octal byte value

\xh, \xhh
(h = 0 - 9, A -
F)

hexadecimal byte value

\uxxxx, \Uxxxxxxxx (x = 0 - 9, A - F)

16 or 32-bit hexadecimal Unicode character
value

Any other character following a backslash is taken
literally. Thus, to include a backslash character, write two
backslashes (\\). Also, a single
quote can be included in an escape string by writing
\', in addition to the normal way of
''.

It is your responsibility that the byte sequences you
create, especially when using the octal or hexadecimal
escapes, compose valid characters in the server character set
encoding. When the server encoding is UTF-8, then the Unicode
escapes or the alternative Unicode escape syntax, explained
in Section
4.1.2.3, should be used instead. (The alternative would
be doing the UTF-8 encoding by hand and writing out the
bytes, which would be very cumbersome.)

The Unicode escape syntax works fully only when the server
encoding is UTF8. When other server
encodings are used, only code points in the ASCII range (up
to \u007F) can be specified. Both
the 4-digit and the 8-digit form can be used to specify
UTF-16 surrogate pairs to compose characters with code points
larger than U+FFFF, although the availability of the 8-digit
form technically makes this unnecessary. (When surrogate
pairs are used when the server encoding is UTF8, they are first combined into a single
code point that is then encoded in UTF-8.)

Caution

If the configuration parameter
standard_conforming_strings is off, then PostgreSQL recognizes backslash
escapes in both regular and escape string constants.
However, as of PostgreSQL 9.1, the default is
on, meaning that backslash
escapes are recognized only in escape string
constants. This behavior is more standards-compliant,
but might break applications which rely on the
historical behavior, where backslash escapes were
always recognized. As a workaround, you can set this
parameter to off, but it is
better to migrate away from using backslash escapes.
If you need to use a backslash escape to represent a
special character, write the string constant with an
E.

PostgreSQL also supports
another type of escape syntax for strings that allows
specifying arbitrary Unicode characters by code point. A
Unicode escape string constant starts with U& (upper or lower case letter U followed
by ampersand) immediately before the opening quote, without
any spaces in between, for example U&'foo'. (Note that this creates an
ambiguity with the operator &.
Use spaces around the operator to avoid this problem.) Inside
the quotes, Unicode characters can be specified in escaped
form by writing a backslash followed by the four-digit
hexadecimal code point number or alternatively a backslash
followed by a plus sign followed by a six-digit hexadecimal
code point number. For example, the string 'data' could be written as

U&'d\0061t\+000061'

The following less trivial example writes the Russian word
"slon" (elephant) in Cyrillic
letters:

U&'\0441\043B\043E\043D'

If a different escape character than backslash is desired,
it can be specified using the UESCAPE clause after the string, for
example:

U&'d!0061t!+000061' UESCAPE '!'

The escape character can be any single character other
than a hexadecimal digit, the plus sign, a single quote, a
double quote, or a whitespace character.

The Unicode escape syntax works only when the server
encoding is UTF8. When other server
encodings are used, only code points in the ASCII range (up
to \007F) can be specified. Both the
4-digit and the 6-digit form can be used to specify UTF-16
surrogate pairs to compose characters with code points larger
than U+FFFF, although the availability of the 6-digit form
technically makes this unnecessary. (When surrogate pairs are
used when the server encoding is UTF8, they are first combined into a single
code point that is then encoded in UTF-8.)

Also, the Unicode escape syntax for string constants only
works when the configuration parameter
standard_conforming_strings is turned on. This is because
otherwise this syntax could confuse clients that parse the
SQL statements to the point that it could lead to SQL
injections and similar security issues. If the parameter is
set to off, this syntax will be rejected with an error
message.

To include the escape character in the string literally,
write it twice.

While the standard syntax for specifying string constants
is usually convenient, it can be difficult to understand when
the desired string contains many single quotes or
backslashes, since each of those must be doubled. To allow
more readable queries in such situations, PostgreSQL provides another way, called
"dollar quoting", to write string
constants. A dollar-quoted string constant consists of a
dollar sign ($), an optional
"tag" of zero or more characters,
another dollar sign, an arbitrary sequence of characters that
makes up the string content, a dollar sign, the same tag that
began this dollar quote, and a dollar sign. For example, here
are two different ways to specify the string "Dianne's horse" using dollar quoting:

$$Dianne's horse$$
$SomeTag$Dianne's horse$SomeTag$

Notice that inside the dollar-quoted string, single quotes
can be used without needing to be escaped. Indeed, no
characters inside a dollar-quoted string are ever escaped:
the string content is always written literally. Backslashes
are not special, and neither are dollar signs, unless they
are part of a sequence matching the opening tag.

It is possible to nest dollar-quoted string constants by
choosing different tags at each nesting level. This is most
commonly used in writing function definitions. For
example:

$function$
BEGIN
RETURN ($1 ~ $q$[\t\r\n\v\\]$q$);
END;
$function$

Here, the sequence $q$[\t\r\n\v\\]$q$ represents a dollar-quoted
literal string [\t\r\n\v\\], which
will be recognized when the function body is executed by
PostgreSQL. But since the
sequence does not match the outer dollar quoting delimiter
$function$, it is just some more
characters within the constant so far as the outer string is
concerned.

The tag, if any, of a dollar-quoted string follows the
same rules as an unquoted identifier, except that it cannot
contain a dollar sign. Tags are case sensitive, so $tag$String content$tag$ is correct, but
$TAG$String content$tag$ is not.

A dollar-quoted string that follows a keyword or
identifier must be separated from it by whitespace; otherwise
the dollar quoting delimiter would be taken as part of the
preceding identifier.

Dollar quoting is not part of the SQL standard, but it is
often a more convenient way to write complicated string
literals than the standard-compliant single quote syntax. It
is particularly useful when representing string constants
inside other constants, as is often needed in procedural
function definitions. With single-quote syntax, each
backslash in the above example would have to be written as
four backslashes, which would be reduced to two backslashes
in parsing the original string constant, and then to one when
the inner string constant is re-parsed during function
execution.

Bit-string constants look like regular string constants
with a B (upper or lower case)
immediately before the opening quote (no intervening
whitespace), e.g., B'1001'. The only
characters allowed within bit-string constants are 0 and 1.

Alternatively, bit-string constants can be specified in
hexadecimal notation, using a leading X (upper or lower case), e.g., X'1FF'. This notation is equivalent to a
bit-string constant with four binary digits for each
hexadecimal digit.

Both forms of bit-string constant can be continued across
lines in the same way as regular string constants. Dollar
quoting cannot be used in a bit-string constant.

where digits is one or
more decimal digits (0 through 9). At least one digit must be
before or after the decimal point, if one is used. At least
one digit must follow the exponent marker (e), if one is present. There cannot be any
spaces or other characters embedded in the constant. Note
that any leading plus or minus sign is not actually
considered part of the constant; it is an operator applied to
the constant.

These are some examples of valid numeric constants:

42
3.5
4.
.001
5e2
1.925e-3

A numeric constant that contains neither a decimal point
nor an exponent is initially presumed to be type integer if its value fits in type integer (32 bits); otherwise it is presumed to be
type bigint if its value fits in type
bigint (64 bits); otherwise it is taken
to be type numeric. Constants that
contain decimal points and/or exponents are always initially
presumed to be type numeric.

The initially assigned data type of a numeric constant is
just a starting point for the type resolution algorithms. In
most cases the constant will be automatically coerced to the
most appropriate type depending on context. When necessary,
you can force a numeric value to be interpreted as a specific
data type by casting it. For example, you can force a numeric
value to be treated as type real
(float4) by writing:

A constant of an arbitrary type can be entered
using any one of the following notations:

type 'string'
'string'::type
CAST ( 'string' AS type )

The string constant's text is passed to the input
conversion routine for the type called type. The result is a constant of the
indicated type. The explicit type cast can be omitted if
there is no ambiguity as to the type the constant must be
(for example, when it is assigned directly to a table
column), in which case it is automatically coerced.

The string constant can be written using either regular
SQL notation or dollar-quoting.

It is also possible to specify a type coercion using a
function-like syntax:

typename ( 'string' )

but not all type names can be used in this way; see
Section
4.2.9 for details.

The ::, CAST(), and function-call syntaxes can also be
used to specify run-time type conversions of arbitrary
expressions, as discussed in Section
4.2.9. To avoid syntactic ambiguity, the type 'string' syntax can only be used to
specify the type of a simple literal constant. Another
restriction on the type 'string' syntax is that it does not
work for array types; use :: or
CAST() to specify the type of an
array constant.

The CAST() syntax conforms to
SQL. The type 'string' syntax is a generalization
of the standard: SQL specifies this syntax only for a few
data types, but PostgreSQL
allows it for all types. The syntax with :: is historical PostgreSQL usage, as is the
function-call syntax.

An operator name is a sequence of up to NAMEDATALEN-1 (63 by default) characters from the
following list:

+ - * / < > = ~ ! @ # % ^ & | ` ?

There
are a few restrictions on operator names, however:

-- and /* cannot appear anywhere in an operator
name, since they will be taken as the start of a
comment.

A multiple-character operator name cannot end in
+ or -,
unless the name also contains at least one of these
characters:

~ ! @ # % ^ & | ` ?

For
example, @- is an allowed operator
name, but *- is not. This
restriction allows PostgreSQL to parse SQL-compliant
queries without requiring spaces between tokens.

When working with non-SQL-standard operator names, you will
usually need to separate adjacent operators with spaces to
avoid ambiguity. For example, if you have defined a left unary
operator named @, you cannot write
X*@Y; you must write X* @Y to ensure that PostgreSQL reads it as two operator names
not one.

Some characters that are not alphanumeric have a special
meaning that is different from being an operator. Details on
the usage can be found at the location where the respective
syntax element is described. This section only exists to advise
the existence and summarize the purposes of these
characters.

A dollar sign ($) followed by
digits is used to represent a positional parameter in the
body of a function definition or a prepared statement. In
other contexts the dollar sign can be part of an identifier
or a dollar-quoted string constant.

Parentheses (()) have their
usual meaning to group expressions and enforce precedence.
In some cases parentheses are required as part of the fixed
syntax of a particular SQL command.

Brackets ([]) are used to
select the elements of an array. See Section 8.15 for more information on
arrays.

Commas (,) are used in some
syntactical constructs to separate the elements of a
list.

The semicolon (;) terminates an
SQL command. It cannot appear anywhere within a command,
except within a string constant or quoted identifier.

The colon (:) is used to select
"slices" from arrays. (See
Section 8.15.) In certain SQL
dialects (such as Embedded SQL), the colon is used to
prefix variable names.

The asterisk (*) is used in
some contexts to denote all the fields of a table row or
composite value. It also has a special meaning when used as
the argument of an aggregate function, namely that the
aggregate does not require any explicit parameter.

The period (.) is used in
numeric constants, and to separate schema, table, and
column names.

A comment is a sequence of characters beginning with double
dashes and extending to the end of the line, e.g.:

-- This is a standard SQL comment

Alternatively, C-style block comments can be used:

/* multiline comment
* with nesting: /* nested block comment */
*/

where the comment begins with /*
and extends to the matching occurrence of */. These block comments nest, as specified in
the SQL standard but unlike C, so that one can comment out
larger blocks of code that might contain existing block
comments.

A comment is removed from the input stream before further
syntax analysis and is effectively replaced by whitespace.

Table
4-2 shows the precedence and associativity of the operators
in PostgreSQL. Most operators
have the same precedence and are left-associative. The
precedence and associativity of the operators is hard-wired
into the parser. This can lead to non-intuitive behavior; for
example the Boolean operators < and
> have a different precedence than
the Boolean operators <= and
>=. Also, you will sometimes need
to add parentheses when using combinations of binary and unary
operators. For instance:

SELECT 5 ! - 6;

will be parsed as:

SELECT 5 ! (- 6);

because the parser has no idea — until it is too late — that
! is defined as a postfix operator, not
an infix one. To get the desired behavior in this case, you
must write:

SELECT (5 !) - 6;

This is the price one pays for extensibility.

Table 4-2. Operator Precedence (decreasing)

Operator/Element

Associativity

Description

.

left

table/column name separator

::

left

PostgreSQL-style
typecast

[]

left

array element selection

+-

right

unary plus, unary minus

^

left

exponentiation

*/%

left

multiplication, division, modulo

+-

left

addition, subtraction

IS

IS TRUE, IS FALSE, IS
NULL, etc

ISNULL

test for null

NOTNULL

test for not null

(any other)

left

all other native and user-defined operators

IN

set membership

BETWEEN

range containment

OVERLAPS

time interval overlap

LIKEILIKESIMILAR

string pattern matching

<>

less than, greater than

=

right

equality, assignment

NOT

right

logical negation

AND

left

logical conjunction

OR

left

logical disjunction

Note that the operator precedence rules also apply to
user-defined operators that have the same names as the built-in
operators mentioned above. For example, if you define a
"+" operator for some custom data
type it will have the same precedence as the built-in
"+" operator, no matter what yours
does.

When a schema-qualified operator name is used in the
OPERATOR syntax, as for example
in:

SELECT 3 OPERATOR(pg_catalog.+) 4;

the OPERATOR construct is taken to
have the default precedence shown in Table 4-2
for "any other" operator. This is
true no matter which specific operator appears inside
OPERATOR().

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